This tool is something that Facebook is trying to sell. To other companies. So you're missing the point with your superficial speculation as to the balance of power between Facebook and its employees.

For that reason, I'll keep the rebuttal short: laws are still valid, as far as I know. And this tool is blatantly illegal. Facebook employees also don't typically face starvation if they can't find a new job right away. And considering how rare unions are in the tech sector, and how common they are in, for example, automotive, my hunch is unionisation is more likely to happen at companies facing economic pressure.